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NIRCAM PUPIL IMAGING LENS MECHANISM AND OPTICAL DESIGN - page 2 / 9

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3-DOF Focus and alignment mechanism (FAM) with pick-off mirror

Focal plane array (FPA)

Pupil imaging lens (PIL)

Beryllium optical bench assembly (OBA) 880 mm x 820 mm

Filter wheel assemblies (FWA)

  • Spectral filters

  • Pupil wheel elements

Figure 1:

Location of the PIL assembly within NIRCam module A bench.

1.2

Driving requirements

There are many challenges in developing an optical mechanism for NIRCam. One difficulty is developing a lens system that alters the science prescription to create the appropriate image with a wavefront error of less than 75% Strehl, and a distortion of less than 2%. Another challenge is developing the optical mounts and the actuating mechanism to operate at 35 Kelvin. The mechanism also needs to perform the insertion repeatably to 40 microns with a maximum of 0.6 milli-Watts of power. There is an additional requirement that has been levied onto the PIL assembly that is unique with respect to all other NIRCam components. The PIL must perform operations in a fail-safe manner and not interfere with the science optics under any reasonable failure. These PIL assembly requirements, along with many others demand a unique opto- mechanical solution.

Optical arm (titanium)

Fail-safe spring

Stowage stop magnets

Position sensor track

PIL bipod mounts to OBA with locking cams

Position sensors

Rotation hard stop

Ø150 mm B.C.

Counterweight (tungsten)

Actuator housing (titanium)

Figure 2:

The PIL assembly with functional call-outs.

125 mm

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